hibernate 所遇到的问题

Q: a different object with the same identifier value was already associated with the session: [com.salary.hibernate.hbm.Role#boss3]

A:查看官方的FAQ:
The session maintains a unique mapping between persistent identity and object instance, in order to help you
avoid data aliasing problems. You cannot simultaneously attach two objects with the same class and identifier
to the same session.

The best way to avoid any possibility of this exception is to always call saveOrUpdate() at the beginning
of the transaction, when the session is empty.

In Hibernate3, you can try using the merge() operation, which does not reattach the passed instance.

(1)也就是说session 中保留着一份"持久化对象"与 "persistent identity"之间的映射表,目的是为了防止data aliasing problems
如果我们在session中重复加载第二个具有相同标示符的 "持久化对象"就会报错
 解决办法: 将所有的saveOrUpdate 方法改为 merge()